In order to get acceptable processing speed from resole resin impregnated substrates, it is common practice to use phenol-formaldehyde resoles which have high molecular weight, that is, they are reacted to near the gel point in the preparation. These materials have to be dissolved in an organic solvent to provide viscosities low enough to be processable. The high viscosity leads to poor resin penetration into many substrates, with the result being certain poorer properties of the finished article such as water absorption and appearance. Also, during resin preparation the resin high viscosity leads to poor heat transfer, longer resin cycles, and molecular weight distribution becomes too broad.
Thus, in accordance with the present invention, resole resin binder compositions are provided with greatly accelerated cure rates that provide laminates having excellent electrical and fire-retardant properties. It has been discovered that the addition of 1 to 30 parts of boron compounds per hundred parts of resole resin solids provides novel binder compositions with great utility. Because of the boron additive, resole resins can be made of low molecular weight and narrow molecular weight distribution giving a more reliable, reproducible resin product in shorter cycles. No organic solvent need be used, eliminating a large pollution contributor. Penetration of this low molecular weight resin into any substrate is excellent. Processing speed is equal or better compared to currently used resole varnishes, and final laminated product properties are better, especially electrical and flame resistance properties.